1. Field of the Invention
This invention relates to a zoom optical system which is peculiarly suitable for an electronic imaging optical system, has a large aperture, and is excellent in imaging performance and an electronic imaging apparatus having this zoom optical system.
2. Description of Related Art
Digital cameras have reached levels of practical use in high pixel density (high image quality) and small-sized and slim designs. As a result, the digital cameras have replaced silver-halide 35 mm cameras with respect to their functions and markets. The next performance requirement is that an object can be clearly photographed even in surroundings in which the amount of light is small. Hence, it is imperatively needed that high imaging performance and small thickness that have been attained so far in optical systems are left as they are and a large aperture ratio is designed.
As a conventional zoom optical system suitable for the design of the large aperture ratio, a positive refracting power lead type zoom optical system has been known. This positive refracting power lead type zoom optical system includes, in order from the object side, a first lens unit with positive refracting power, a second lens unit with negative refracting power, a third lens unit with positive refracting power, and a fourth lens unit with positive refracting power.
On the other hand, as a zoom optical system suitable for a slim design, a negative refracting power lead type zoom optical system has been known. This negative refracting power lead type zoom optical system includes, in order from the object side, a first lens unit with negative refracting power, a second lens unit with positive refracting power, and a third lens unit with positive refracting power.